First you need to start by gathering information about what your website should do (gather system requirements).
Then you should choose a technology for web development that will fit your website's requirements, and that you and your team is comfortable using (or learning).
If your website is static (simply displays information to the user that is not stored in a database), and you don't know HTML/CSS intimately, you only need to find some tools that will help you design the website (like Dreamweaver or something).
If your website is dynamic (does something other than just displaying information to the user) you will need to choose a Server-Side platform to handle your requirements (ie: retrieving data from a database, saving data to a database or otherwise processing information). This could be any technology like ASP.NET, Java, PHP...etc. etc. etc.
Choose this technology based on your team's strengths and knowledge base.
Keep in mind that there are a lot of per-packaged website building platforms out there already that may do the job for you. Like wordpress for a blog... if that's what your website requirements entail.